There are many systems that are designed so that a projectile, such as a shell, a rocket or, again, a missile reaches an objective or target such as an aircraft, a helicopter or a tank. These systems differ from one another according to the target to be reached and according to the projectile used. Thus, for a high-speed target such as an aircraft, it is preferred to use a self-guided missile which, after being launched towards the target, moves by itself towards the target in modifying its initial trajectory by means of pieces of information supplied to it by an onboard radar, the antenna of which is pointed towards the target.
Self-guided missiles such as this give satisfactory results, but cost very much, and their cost is acceptable only for the destruction of even costlier targets located at relatively big distances of more than five kilometers. Beyond this distance, it is often the practice to use missiles or rockets that are directed towards their objective by means of pieces of information provided by the firing station, these pieces of information having the purpose of preserving the firing station-missile-target alignment irrespectively of the movements of the latter.
Shells fired by guns or mortars are also used, and have the advantage of being inexpensive and light, of having a high initial velocity and of being capable of being fired at a high rate. However, they have the major drawback wherein their trajectory, which is ballistic, can no longer be modified after they are launched. The result thereof is that hits are less frequent than with guided missiles, for the target may move erratically during the trajectory of the shell. Furthermore, the real trajectory of the shell may be different from the theoretical trajectory, owing to the variation in certain parameters such as the speed and direction of the wind, the quality of the solid propellent etc.
To improve the hitting efficiency of shells, as well as that of missiles and rockets, notably against so-called light targets, namely targets with relatively little shielding, these projectiles are provided with "proximity fuses" which set off the explosive charge when they pass in the vicinity of the target. To be efficient, the charge must explode at a relatively small distance, for example a distance of a few meters; now, with the uncertainties of the trajectory of the projectile and of the movement of the target, the projectile often goes to a distance which is greater than the planned triggering value.
An object of the present invention, therefore, is to make a system enabling a modification of the trajectory of a projectile, notably a shell, launched towards a target in such a way that it reaches it or passes by at a distance that is small enough for the explosion provoked by its charge to definitely destroy the target.
The French patent application No. 2 129 948, describes a prior art guidance system comprising,
a radar emission and reception means to measure the position and radial velocity of the objective and of the projectile,
a computation means to compute a nominal trajectory of the projectile, such that it reaches the objective, as well as its real trajectory, on the basis of pieces of information on position and radial velocity of the objective and the projectile,
a computation means to compute the deviations between the real trajectory of the projectile and its nominal trajectory,
a computation means to compute the corrections to be applied to the real trajectory of the projectile so that the projectile reaches the objective,
a radio transmitter to transmit the corrections to be applied to the projectile and
a radio reception means and control means to apply the correction systems, placed on board the system.
This system has the drawback of being sensitive to radio jamming signals emitted by the objective aimed at.